Audio certainly isn't the only aspect of music that's copyrighted, and lyrics are no exception. As reported by billboard.com, it seems The National Music Publishers Association has issued take-down notices to 50 lyrics sites believed to be operating without proper licensing. These notices require the sites in question to either obtain licenses or remove all copyrighted content.

"This is not a campaign against personal blogs, fan sites, or the many websites that provide lyrics legally," clarified David Israelite, Chief Executive of the NMPA. "The NMPA is targeting fifty sites that engage in blatant illegal behavior."

According to an October report by University of Georgia researcher David Lowery, there are more than five million lyric searches on Google every day, and 50% of the top results come from unlicensed sites. For example, the unlicensed lyricsmania.com, which runs ads, has 12 million unique visitors a month. There are large amounts of potential advertising dollars here.

"Based on the popularity of lyric searches, it is possible that unlike the sound recording business, the lyric business may be more valuable in the Internet age," Lowery writes. "Indeed, the vast majority of these websites seem to have well established monetization schemes based on advertising. Many of the sites appear to have accounts with major online advertising exchanges and prominently feature advertising from!major brands. There are even companies that appear to specialize in matching specific lyrics to key demographics for advertisers."

According to Israelite, the take-down notices are "a precursor to filing copyright infringement lawsuits". Last year, the NMPA, who operate on behalf of Bug Music Warner, Chappell Music and Peermusic, won a $6.6 million judgement against LiveUniverse, a company that operated unlicensed lyrics sites. In 2010, they successfully sued Motive Force, the company that operated LyricWiki, and received "an undisclosed amount of funds associated with the exploitation of the unauthorized content."

That's all for now. Peep the list of targeted sites below. Thankfully, our collaborators at gotbars.com have flown under the radar for the time being.